Congrats to your son on his trophy! Regarding the water bugs, if they look like fleas, they may be water fleas, Daphnia. If so, they are invertebrates found in most fresh water lakes, especially green water as they feed on algae.

Water fleas are an important waterfowl food source, especially in waterfowl hatchlings and hen laying northern shovelers, gadwalls and mallards. Molting drake mallards also eat water fleas.

Logically this suggests that while waterfowl such as mallards mainly get nutrition from plants, during times of growth for hatchlings, hens laying eggs and feather regeneration for drakes, they need animal protein as well.

In the circle of life, in the Delta Marsh at Lake Manitoba, the peak population of Daphnia coincides with the peak ducking hatch. While adult waterfowl feast on vegetation in the same marsh, hatchlings get their nutrition from animal protein by consuming invertebrates such as Daphnia. As you’ve noticed in your own duck pond, adults will eat Daphnia but may prefer vegetation if available.

Daphnia is also like the canary in the mine. They are fragile when it comes to pollutants and used in research to detect chemicals in fresh water sources.

For those interested in elevating their waterfowl knowledge, here are a couple of interesting studies on waterfowl selective feeding habits.

Those look a bit like scuds as well. I don't know what the scientific name is, but if you search "scud fly fishing" you'll see what I'm talking about. Fly fisherman use a pattern that looks something like that.